MDRaid 1 Recovery

[Bruno Wolff III]

On Sat, May 02, 2009 at 19:17:32 -0400,
  Law Barstow <LBarstow at cfl.rr.com> wrote:
> not in the system, leaving Drive 1.  When I try to boot, I get just a
> message of "GRUB".  I'm assuming that my problem is that GRUB was
> installed to drive 0 and drive 0 was set to be my primary.  

At the grub prompt you can try something like:
configfile (hd1,0)/grub/grub.conf
If /boot is the first partition on the drive this should work. It is
a later one increase the second 0.
This also assumes the bad drive is still be detected by grub so that the
good drive is known to it as hd1.

You could also pull the bad drive.

> How do I resolve the problem booting to drive 1?  Second, once I install
> my replacement device, how do I rebuild the array?  I assume I'll need
> to some how get my current Drive 1 set to primary and then install the
> second drive, and use mdadm to add it. 

Use some partitioning tool to create a software raid partition the same
size as the previous one. (If the drive is the same size as the other one,
you might just copy of the partition table.) You can add the partition
as an element in the array using mdadm. It would be something like:
mdadm /dev/md0 -a /dev/sda1
You need to do that for each array. Typically /boot and / are separate arrays.